The subhorizon circle is a white circle of light that runs parallel to the horizon at the level of the
subsun. In
contrast to the
horizon circle, the subhorizon circle is located exclusively below the horizon. For this reason, there are very few sightings, as this type of halo can only be observed from an elevation (e.g. mountain) or from an airplane.
In
oriented plate crystals, multiple light paths with internal reflections are possible, contributing to the subhorizon circle and whose overall superposition provides a realistic image of this halo type. Also involved are light paths similar to the Liljequist parhelia, which is why the term "Liljequist subparhelia" appears in the literature. In contrast to the horizontal circle above the horizon, there are hardly any intensity contributions to the area between the
subparhelia, i.e., left and right of the sub-sun. Thus, the subhorizon circle has a gap there. To a lesser extent, parry-oriented column crystals can also contribute to the subhorizon circle.
